A group of Chinese companies will file an appeal Monday against a recent court decision giving Pfizer Inc., the world's largest drug maker, the right to be the sole seller in China of its impotence drug Viagra.

"We will fight this decision," Wang Wei, a lawyer representing the 13 drug makers, said. The companies will file the appeal with a municipal court in China's capital.

Pfizer won an appeal in a Beijing court on June 2 that reinstated its patent on Viagra, which is used by 23 million men worldwide and produced global sales of $1.6 billion for the company last year. That decision overturned a 2004 ruling by China's intellectual property office that withdrew Pfizer's patent, giving Chinese drug makers the right to make a generic version of Viagra.

Pfizer will fight the appeal, Victor Zhou, a spokesman for the New-York based company, said.